Brightness Error

[Guest]

Everytime when I select Kubuntu on GRUB, my brightness come back to 0%.
I tried with lightdm, mdm and kdm, and anyone works.
To fix it I need edit a line of /etc/default/grub
from
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
to
GRUB_CMDLINE_LINUX_DEFAULT="quiet acpi_osi=linux acpi_backlight=vendor splash"
and run update-grub

however if I do this when I turn off my computer, 2 error repport appear. (akonadi, and another process)

this error is not serious, but can prevent a scheduled shutdown and is so ugly pop up error messages

How can I fix it?

Thank you for all help and sorry for my english.

[vinnywright]

you put your edits in between quiet and splash try leaving them together as in ,,,, "quiet splash acpi_osi=linux acpi_backlight=vendor " or remove "quiet splash" to see all the boot up text .

VINNY

[Guest]

you put your edits in between quiet and splash try leaving them together as in ,,,, "quiet splash acpi_osi=linux acpi_backlight=vendor " or remove "quiet splash" to see all the boot up text .

VINNY

thank you for help, but

after de update-grub, I turn off 5 times my computer, 3 times with errors, and 2 times ok.

Erros always appear together:

first: plasma desktop PID:2104, Segmentation fault (11)
second: akonadi_nepomuk_feeder crashs
third:kmix crashs PID2287, Segmentation fault (11)